The invention relates to a process and an arrangement for controlling the temperature of any solid, liquid or gaseous medium. In the case of processes and arrangements of this type, the temperature to be controlled is influenced in an appropriate manner by at least two energy-consuming units, such as the cooling fans, the circulation pumps of a cooling or heating circulation system, chillers, etc. such that the temperature is controlled in the respective desired manner; for example, is adjusted to the desired value. The medium whose temperature is to be controlled may, in particular, be a liquid/gaseous coolant or refrigerant of a cooling or air-conditioning system or a heating fluid of a heating circulation system, but also any component whose temperature is to be maintained at a certain value or within a certain range. A contemplated field of application is the control of the cooling water temperature of a water-cooled motor vehicle engine or the control of the temperature of the engine itself; that is, of the engine block, or of critical points in the engine, for example, the temperature of the valve web.
A process and an arrangement of this type for controlling the coolant temperature of an internal-combustion engine, particularly of an internal-combustion of a motor vehicle, are described in German Patent Document DE 195 08 102 C1, in the case of which at least one coolant pump and a cooling fan are used as energy-absorbing, temperature-influencing units. A control unit controls the coolant temperature to a predeterminable desired value by a corresponding adjustment of the rotational speed of the pump and the fan. In this case, the control unit compares the time-related efficiencies caused, on the one hand, by the operation of the coolant pump and, on the other hand, by those of the fan, for the heat transmission between the fan air flow and the coolant on a cooler module. For this purpose, a gradient method is used in that the heat transfer coefficient for the cooler module is determined, and the partial derivations of the coefficient are, on the one hand, formed according to the coolant flow generated by the pump and, on the other hand, according to the air flow generated by the fan and are used as a measurement for the respective time-related efficiency. These time-related efficiencies are analyzed in that, in the respective operating position, on the basis of the momentary operation point of the coolant circulation system, a step-by-step search takes place for a possibly more favorable operating point in that the quotients of the time-related efficiency to the power consumption for the fan and the pump are compared and, according to which quotient is larger, the air flow or coolant flow is increased. It is known that gradient methods of this type do not ensure that the absolutely most favorable operating point is reached since also an only locally most favorable operating point represents a stable point for this method.
In the case of systems with two power-consuming components by means of which a certain physical quantity can be influenced, it is known to determine in the pertaining output diagram characteristic curves of a respective constant value of the physical quantity and to determine, for the respective momentary value of the physical quantity, by a tangent formation, the pertaining point of the minimal overall power expenditure for the two components. In the conference contribution by P. Ambros and U. Essers, "Simulation Program for Design and Optimization of Engine Cooling Systems for Motor Car", ISATA Conference, Sep. 13, 1993 to Sep. 17, 1993, Aachen, this was described with respect to a coolant circulation system of a motor vehicle engine in that, for a given coolant temperature, the minimal sum of the power consumption of cooling air fan is found, on the one hand, and that of a cooling water pump is found, on the other hand. For this purpose, the characteristic curves of the constant coolant temperature are determined in the two-dimensional output diagram and then the point of the minimal overall output for the given coolant temperature is determined by means of the tangent formation with the straight line of the constant overall output as the tangent. In this case, each characteristic curve of the constant coolant temperature may vary as the function of the system condition, that is, of vehicle condition parameters, such as the outside temperature, the vehicle speed, the engine load, etc.
An object of the invention is to provide a process and an arrangement of the initially mentioned type by means of which and by means of relatively low real-time computing expenditures in each operating condition of the system the medium temperature can be reliably controlled with the lowest possible energy consumption and particularly can be maintained at a defined desired value in a controlled or regulated manner.
This and other objects have been achieved according to the present invention by providing a process for controlling the temperature of a medium, the temperature of the medium to be controlled being influenceable by at least two energy-consuming units, at least one of the energy-consuming units having a controllable output, wherein the output of each of the energy-consuming units is adjusted according to a previously determined energy-minimal characteristic diagram which indicates for each system condition the operating point of an absolutely minimal overall energy consumption of the units for controlling the temperature according to a respective desired temperature value.
This and other objects have been achieved according to the present invention by providing an arrangement for controlling the temperature of a medium, comprising: at least two energy-consuming units for influencing the temperature of the medium to be controlled, at least one of the energy-consuming units having a controllable output, and a control unit which adjusts the output of each of the energy-consuming units according to a previously determined, energy-minimal characteristic diagram which indicates for each system condition the operating point of the absolutely minimal overall energy consumption of the units for controlling the temperature according to a respective desired temperature value.
According to the invention, the output of each of the energy-consuming units provided for influencing the temperature to be regulated is adjusted according to a previously determined, characteristic energy-minimal diagram which indicates for each system condition, including a respective desired value of the temperature to be regulated, the operating point of the absolute minimal overall energy consumption of the energy-consuming units. As the result of this predetermined characteristic diagram, the control unit which carries out the temperature control, after the momentary system condition is sensed, is immediately provided with the information concerning the operating point for the energy-consuming units which is energy-minimal in this condition, which is always an absolute energy minimum. This permits a comparatively fast reaction of the temperature control to changes of the system condition. Because of this global energy minimizing method, it is ensured that the adjusted operating point corresponds not only to a local energy minimum but to the absolute energy minimum in the corresponding system condition.
According to further advantageous developments of the present invention, a checking of the previously determined energy-minimal characteristic diagram is provided at defined time intervals in that, for at least one reference system condition, an energy minimum determination is carried out according to the above-mentioned conventional tangent method in the case of which, after the detection of the momentary system condition, the isothermal line pertaining to the desired value of the temperature to be regulated is determined in the power or energy consumption diagram of the energy-consuming units and then the pertaining tangent or tangent plane of the constant minimal overall energy consumption is determined. This determined energy-consumption minimum is compared with the energy consumption minimum filed in the characteristic diagram for the corresponding reference system condition, whereupon the characteristic diagram can be appropriately corrected depending on the result of the comparison.
According to certain preferred embodiments, the present invention is used for controlling the coolant temperature of a cooling circulation system, for example, for a motor vehicle engine, and contains one or several energy-consuming units which influence the coolant temperature and which have the form of an output-controllable coolant circulation pump and/or of an output-controllable fan whose cooling air flow can act on a cooler of the cooling circulation system. By way of the control unit, the pump and/or the fan are operated such that, on the one hand, the coolant temperature is controlled in the desired manner and, on the other hand, the overall energy consumption of the temperature-influencing units is minimal.
According to certain preferred embodiments, the present invention is used for controlling the coolant temperature of a cooling circulation system provided in a motor vehicle, for example, for cooling an internal-combustion engine, and contains, as one of the power-consuming units, a shutter by means of which the throughput of a ram pressure cooling air flow for a cooler of the cooling circulation system can be variably adjusted with a driving-power-influencing effect on the aerodynamic drag of the vehicle. In this case, the power consumption related to the shutter does not primarily result from the energy expenditure operating the latter but from the fact that, depending on how much air is withdrawn as a cooling air flow for the cooler from the ram pressure range which forms increasingly at a higher vehicle speed, the aerodynamic drag and thus the energy expenditure required for the moving of the vehicle will fluctuate. The use of the shutter therefore allows a controlling of the coolant temperature which is optimized with respect to a minimal overall energy consumption also in the range of higher driving speeds in which the cooling air flow against the cooler can be caused by the ram pressure without the requirement of activating a fan for this purpose.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.